The present invention relates to a rotary recliner for mounting an adjustable seat back to a body supporting seat cushion and in particular to improvements in such a recliner which eliminate the free play between the recliner components when the recliner is not being adjusted.
Rotary recliners for adjustable vehicle seats which employ a pair of mating gears, an inner gear and an outer gear rotating about a common pivot, are well known. Such recliners have a first component attached to the body supporting seat cushion and a second component attached to the seat back. The two recliner components are coupled together for rotation relative to one another about a pivot shaft. One recliner component carries an inner spur gear, having outwardly extending teeth, while the other component carries an outer gear having inwardly directed teeth. The inner gear has at least one less tooth than the outer gear and has a diameter which is smaller than the diameter of the outer gear by at least the radial height of the outer gear teeth.
The inner gear is mounted on an eccentric so as to bias the inner gear in one direction radially relative to the outer gear. This results in meshing of gear teeth on one side and a clearance between the gear teeth on the opposite side. Rotation of the eccentric causes the area of teeth mesh to move circumferentially around the outer gear whereby the difference in the number of gear teeth produces rotation of the inner gear relative to the outer gear.
After adjustment of the seat back, the seat back is held in its adjusted position by the eccentric maintaining the meshing of the inner gear and outer teeth. The recliner is self locking in the sense that forces applied to the seat back can not cause a rotation of the eccentric and movement of the seat back. Only rotation of the eccentric by the operating handle produces a change in the seat back position. A certain amount of free play, i.e. clearance between the gear teeth is necessary for proper operation of the recliner. However, the free play also results in judder, jerking of the seat back during rearward adjustment as well as rattling and vibration of the seat back during vehicle operation on rough roads. Both the judder and the vibration are viewed as evidence of poor quality.
Various approaches have been taken to eliminate the free play from rotary recliners once they have been adjusted. One approach to eliminate free play is to use an axially moving cone which forces the teeth of the inner gear into firm engagement with the outer gear. An example of this is shown in U.S. Pat. No. 4,453,767. The eccentric is formed with a conical outer surface. The inner gear mounted on the eccentric has a complementary conical bore. The eccentric is biased axially by a spring to firmly engage the inclined conical surfaces. One disadvantage of this design is its high friction. The conical surfaces are also bearing surfaces with relative rotational motion as the eccentric is turned to adjust the recliner. The resulting force required to adjust the recliner is high. As a consequence, in a seat having dual recliners, only one recliner will have free play reduction to keep the adjustment efforts acceptable.
Another type of free play reduction is disclosed in U.S. Pat. No. 5,154,475. There a pair of circumferential wedge elements surround a rotary motion transmitting member and form the outer surface of the eccentric. A spring biases the two wedge elements in opposite directions in a generally sickle shaped clearance where the wedge elements tightly fit between the motion transmitting member and the gear. This design also has the disadvantage of high friction caused by engaged wedge surfaces at bearing surfaces with relative motion during recliner adjustment. With this design, one of the two wedge elements remain engaged during adjustment of the recliner, producing a high adjustment force which is substantially constant over the full range of seat back angles.
It is an object of the present invention to provide an improved recliner which is easy to construct, eliminates high friction bearing surfaces during adjustment and which has high strength to resist loads during a vehicle collision.
The recliner of the present invention utilizes a pair of circumferentially spaced, axial movable, wedge segments having an inclined surface which mates with an inclined surface of the eccentric. The wedge segments force the inner gear into tight engagement with the outer gear. The wedge segments are axially movable upon rotary motion of the operating cap. During adjustment, to the free play reduction is first released (i.e. the wedge segments are moved axially) and then the recliner is adjusted by rotation of the eccentric. Since the free play reduction is released before the recliner is adjusted, the adjustment efforts are approximately the same as for a rotary recliner without free play reduction. The lower adjustment efforts are achieved by separating the inclined wedge surfaces from the load bearing surfaces with relative motion during adjustment. The torque required to first release the wedge segments is less than the adjustment torque so that the wedge segments are first released before the recliner is adjusted.
The two wedge segments are circumferentially spaced apart from one another with one wedge segment to each side of the point of maximum eccentricity of the eccentric. The wedge segments are disposed in cutout sections in the eccentric. The optimum location for the wedge segments is 45.degree. to each side of the maximum eccentricity. It is at these two locations that the radial forces of the seat back load act on the eccentric. By placing the wedge segments at these two locations, the radial free play reduction forces are aligned with the seat back load on the eccentric. However, since this is the location of the seat back forces on the eccentric, it is desirable to locate the cutout sections of eccentric elsewhere in order to maintain the thickness of the eccentric and maximize its strength. As a result, in the preferred embodiment, the wedge segments are spaced only 70.degree. apart, 35.degree. to each side of maximum eccentricity. This location produces the desired free play reduction while maintaining the strength of the eccentric.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.